Sparking plugs for internal combustion



J. A. LAIRD 2,734,143

SPARKING PLUGS FOR INTERNAL COMBUSTION ENGINES Feb. 7, 1956 Filed Feb. 17, 1953 ,Znvezvtop QIJZLQL'PCZ/ United States Patent SPARKING PLUGS FOR INTERNAL COMBUSTION ENGINES John Andrew Laird, Coventry, England, assignor to Joseph Lucas (Industries) Limited, Birmingham, England Application February 17, 1953, Serial No. 337,327

Claims priority, application Great Britain February 18, 1952 2 Claims. (Cl. 313-431) This invention relates to sparking plugs for internal combustion engines of the so-called low-voltage type in which the spark discharge occurs over a surface between a pair of electrodes at a voltage of for example about 2 kv. It has been found that under some working conditions sparking may fail to occur owing to a temporary accumulation of oil on the conductive path, or other cause, and the object of the invention is to obviate failure of ignition.

This invention comprises a plug of the type aforesaid having a pair of additional electrodes forming between them an air gap across which a spark can occur at a higher voltage than that required to produce a spark at the semiconductive path.

The accompanying drawing illustrates one embodiment of the invention.

Referring to the drawing, the insulated electrode a of the plug is separated from an annular electrode b by a sleeve 0 of insulating material. The spark normally occurs between these electrodes across the exposed end surface of the sleeve 0. The end of the annular electrode b remote from the spark gap is connected to the body part d of the plug, either integrally or otherwise, and this electrode is surrounded by an annular gas pocket e situated between it and the body part d, the pocket being open at the end adjacent to the spark gap. The electrical connection between the electrode 11 and the body part is efiected by a flange g on the said electrode which abuts against a shoulder h in the body part.

According to the invention there is provided between 2,734,143 Patented Feb. 7, 1956 the insulated electrode a and the body part d an air gap adapted to allow a spark to occur at a higher voltage than that required to produce a spark across the normal path.

The additional gap may be formed as shown between a pair of sparking tips i, 1' attached to the body part and the insulated electrode respectively, or in any other convenient manner.

The arrangement is such that normally the sparking occurs at the low-voltage path. But in the event of failure, the sparking occurs at the air gap at a higher voltage, and continues at this gapuutil the normal condition at the other gap is restored by the action of flame in the engine cylinder on the oil or other deposit. With the resumption of the normal condition, the sparking occurs between the other electrodes. I

By this invention stopping of the engine by failure of the normal sparking is obviated in a simple andreliable manner.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

l. A sparking plug comprising in combination a body part, a pair of main electrodes one of which is of annular form and surrounds a part of the other, a sleeve of insulating material separating the main electrodes, and having an exposed end surface forming between the main electrodes a semi-conductive path across which sparking normally occurs, and a pair of additional electrodes forming between them an air gap across which sparking can temporarily occur, at a higher voltage than that required to produce normal sparking, in the event of failure of normal sparkingdue to an abnormal condition of the semi-conductive path.

2. A sparking plug as claimed in claim 1 and having between the annular main electrode and the body part of the plug, an annular gas pocket which is open at the end adjacent to the semi-conductive path between the main electrodes.

References Cited in the file of this patent UNITED STATES PATENTS 1,962,669 Parkin,Jr June 12, 1934 FOREIGN PATENTS 981,678 France Jan. 11, 1951 

